update build_tests_spec to invoke rscons in a subprocess for each test

build_tests/custom_builder/Rsconsfile

@@ -0,0 +1,16 @@
+class MySource < Rscons::Builder
+  def run(target, sources, cache, env, vars)
+    File.open(target, 'w') do |fh|
+      fh.puts <<EOF
+#define THE_VALUE 5678
+EOF
+    end
+    target
+  end
+end
+
+Rscons::Environment.new do |env|
+  env.add_builder(MySource.new)
+  env.MySource('inc.h', [])
+  env.Program('program.exe', Dir['*.c'])
+end

build_tests/custom_builder/cvar_expansion.rb

@@ -0,0 +1,18 @@
+class MySource < Rscons::Builder
+  def run(target, sources, cache, env, vars)
+    File.open(target, 'w') do |fh|
+      fh.puts <<EOF
+#define THE_VALUE 678
+EOF
+    end
+    target
+  end
+end
+
+env = Rscons::Environment.new do |env|
+  env["hdr"] = "inc.h"
+  env["src"] = "program.c"
+  env.add_builder(MySource.new)
+  env.MySource('${hdr}')
+  env.Program('program.exe', "${src}")
+end

build_tests/custom_builder/cvar_lambda.rb

@@ -0,0 +1,28 @@
+class MySource < Rscons::Builder
+  def run(target, sources, cache, env, vars)
+    File.open(target, 'w') do |fh|
+      fh.puts <<EOF
+#define THE_VALUE #{env.expand_varref("${the_value}")}
+EOF
+    end
+    target
+  end
+end
+
+e1 = Rscons::Environment.new do |env|
+  env.add_builder(MySource.new)
+  env["one"] = "5"
+  env[:cfg] = {val: "9"}
+  env["two"] = lambda do |args|
+    args[:env][:cfg][:val]
+  end
+  env["the_value"] = lambda do |args|
+    "${one}${two}78"
+  end
+end
+
+e1.clone do |env|
+  env[:cfg][:val] = "6"
+  env.MySource('inc.h', [])
+  env.Program('program.exe', Dir['*.c'])
+end

build_tests/custom_builder/multiple_targets.rb

@@ -0,0 +1,19 @@
+class CHGen < Rscons::Builder
+  def run(target, sources, cache, env, vars)
+    c_fname = target
+    h_fname = target.sub(/\.c$/, ".h")
+    unless cache.up_to_date?([c_fname, h_fname], "", sources, env)
+      puts "CHGen #{c_fname}"
+      File.open(c_fname, "w") {|fh| fh.puts "int THE_VALUE = 42;"}
+      File.open(h_fname, "w") {|fh| fh.puts "extern int THE_VALUE;"}
+      cache.register_build([c_fname, h_fname], "", sources, env)
+    end
+    target
+  end
+end
+
+Rscons::Environment.new do |env|
+  env.add_builder(CHGen.new)
+  env.CHGen("inc.c", ["program.c"])
+  env.Program("program.exe", %w[program.c inc.c])
+end